1. Field of the Invention
This invention relates to a method of directly welding pieces of dissimilar metals and, more particularly, to a method of welding an aluminum bronze socket with a stainless steel casing and Bourdon tube without the use of a filler or insert material. This invention also relates to the articles manufactured by such method.
2. Description of the Prior Art
Pressure gauges and the like are widely used and commercially available from a great variety of manufacturers. Because of their extensive commercial and industrial uses, such pressure gauges are high-production items and are sold in very price-conscious competition. To be competitive, each manufacturer is continually attempting to reduce production costs by any improvements, however marginal, which may reduce either the labor or materials costs or both while still maintaining product quality and performance.
Pressure gauges normally include a socket by which they may be releasably coupled with the container of fluid under pressure to be measured. The socket is normally fabricated of a long-life material, such as aluminum bronze, which is resistant to the corrosive effects of the fluid whose pressure is being measured. Threads are formed on the outward end of the socket for coupling and uncoupling the socket and gauge with a fluid container such as a tank, pipe, or the like. The central section of the socket is normally provided with one or more flat areas for receiving a wrench to facilitate the coupling and uncoupling of the gauge with respect to the container. Adjacent the other or inward end, the gauge permanently receives the Bourdon tube and casing. Within the casing, are the pressure sensing mechanisms which include the Bourdon tube. Casings and Bourdon tubes are frequently formed of stainless steel, a ferrous alloy which is highly resistant to corrosion, provides long life to the piece, and maintains a good appearance to an observer of the gauge.
Many techniques have been utilized for effecting the casing-to-socket coupling. It is well known to utilize adhesives, elastomeric seals, and other mechanical devices. Such mechanical devices are characterized by less than the desired reliability along with high costs in terms of both materials and workmanship. Welding the joint is likewise well known. Welding, however, normally is acheivable only with pieces of the same or metallurgically similar metals or by introducing a filler or insert material or metal between the dissimilar metals being welded.
The patent literature describes various approaches for coupling both sockets with casings and sockets with Bourdon tubes. Note, for example, U.S. Pat. Nos. 2,125,016 to Gruver; 3,005,867 to Green et al; 4,384,490 to Bissell; and 4,543,833 to Ferguson.
Welding is generally accepted as the preferred technique for coupling both sockets with casings and sockets with Bourdon tubes. The welding process provides a strong, long lasting, fluid tight coupling. However, welding has found limited usage in pressure gauge applications because the preferred materials to be coupled have dissimilar metallurgical properties. All known technical publications on the subject of welding dissimilar metals suggest that stainless steel, a preferred metal for casing and Bourdon tubes, and aluminum bronze, a preferred metal for sockets, cannot be welded directly, but only through the use of a insert or material. Consider, for example: (1) American Society for Metals' Metals Handbook, 9th Edition, Volume 6, pages 414-424; (2) CDA Abstract #19297 of Macken, P.J., and Smith, A.A., CDA, United Kingdom "JOINING PROCESSES" Chapter 20 from THE ALUMINUM BRONZES Second Edition, CDA Publication No. 31, Copper Dev Assn, London (1966), 162-178; (3) CDA Abstract #17120 of Wirtz, H., Duisburg, Germany THE SIGNIFICANCE AND USE OF INTERMEDIATE LAYERS DURING WELDING AND METAL SPRAYING OF DISSIMILAR METALS Schweissen and Schneiden, 22 (10), 417-421 (Oct. 1970), (10 FIG., 19 ref.); (4) CDA ABSTRACT #4095 of Kocher, Reiner, Schweissfachingenieur and Leiter der Qualitatsstelle bei der Firma Carl Canzler, Duren, Germany PROPERTIES AND WELDING TECHNIQUES OF COPPER AND COPPER ALLOYS TECHNISCHE UBERWACHUNG, 9 (7), 219-223 (1968), (8 FIG., 11 tables); (5) CDA Abstract #23325 of Mendolia, J., and Mauneau, A., Inst Natl des Sciences Appliquees, Rennes, France WELDING COPPER AND STAINLESS STEEL FOR CRYOGENIC AND VACUUM SYSTEMS Cryogenics, 20 (6), p. 336 (Jun. 1980), (1 FIG. ); (6) Solomon, D,E., University of Michigan, Ann Arbor, Mich. JOINTING DISSIMILAR METALS BY GAS TUNGSTEN-ARC BRAZE-WELDING Welding Journal, 47 (3), 118-184, 189-191 (Mar. 1968), (16 FIG., 1 Table); and (7) WELDING HANDBOOK, Volume 4, 7the Edition, "Specific Dissimilar Metal Combinations", p. 535.
Note, in particular, the last cited article which suggests that a filler material is required for the welding of aluminum bronze to stainless steel.
Even the patent literature fails to teach or suggest the welding of aluminum bronze to stainless steel in the absence of a filler or insert material. Consider U.S. Pat. Nos. 1,779,278 to Kalschne; 2,769,231 to Grenell; 2,914,641 to Yuhasz; 2,937,438 to Lemon; 3,119,632 to Skinner; 3,257,710 to Brown et al., 3,287,540 to Connelly; 3,614,379 to Troton; 3,728,783 to Chartet; and 4,407,441 to Aarts.
Note, in particlar, the patent to Troton which suggests the need for a filler material for joining aluminum bronze to stainless steel.
By way of background, the process of welding is a metal joining process wherein coalescence is produced by heating to suitable temperatures to melt together the base metals with or without the addition of filler metal. If filler metal is used, it shall have a melting point and composition approximately the same as the base metal. Variations of the welding process are brazing and soldering. Brazing is a metal joining process wherein coalescence is produced by use of nonferrous filler metal having a melting point of above 800.degree. Fahrenheit (425.degree. Centigrade), but lower than that of the base metals joined. Soldering is a metal joining process wherein coalescence is produced by heating to suitable temperature and by using a nonferrous alloy fusible at temperatures below 800.degree. Fahrenheit (425.degree. Centigrade) and having a melting point below that of the base metals being joined.
While welding is normally the preferred method for coupling metals in applications such as pressure gauges, the weld line between the metals being coupled can often constitute the major area of weakness in the welded article. When welding with a filler or insert material between the pieces being coupled, two such weld lines of potential weakness are created. In addition, welding without a filler or insert material minimizes the cost of coupling the pieces by eliminating one element from both the process as well as the final product. Welding without a filler or insert material also reduces the method steps and technical skills required on the part of the person performing the welding. Welding without a filler or insert material also renders the process more succeptible to being carried out automatically or semi-automatically. As can be readily understood, welding without a filler or insert material is normally proferred whenever possible or technically feasible.
As illustrated by the great number of prior patents and technical publications, efforts are continuously being made in an attempt to solve the problem of directly welding stainless steel to aluminum bronze and like metals in the absence of a filler or insert material. None of the known patents or technical publications, however, discloses or suggests the present inventive combination of method steps as disclosed herein for reliably, conveniently, accurately and economically welding such dissimilar metals, nor do they disclose or suggest the inventive acticles fabricated from the application of such method steps. The present invention achieves its purposes, objectives, and advantages over the prior art through a new, useful, and unobvious combination of method steps and component elements, with a minimum number of functioning parts, at a reduction of cost for both parts and labor, and through the utilization of only readily available materials and conventional components.
These purposes, objectives, and advantages should be construed as merely illustrative of some of the more prominent features and applications of the present invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other purposes, objects, and advantages as well as a fuller understanding of the invention may be had by referring to the summary of the invention and detailed description describing the preferred embodiment in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.